IMS (Internet Protocol Multimedia Subsystem) is a standardized service delivery architecture that provides IP-based mobile and fixed multimedia services to IMS subscribers. IMS allows operators of different network types with varying architecture to offer the same services to all of their subscribers.
IMS subscribers, typically, access an IMS network via an access network using a UE (User Equipment). A UE is a device that has IP connectivity and is capable of requesting an IP address from the IMS network. A UE negotiates QoS (Quality of Service) requirements and other capabilities during a communication session setup process. Typically, a UE can negotiate the media type, traffic direction, bit rate, packet size, and bandwidth, for example.
Each IMS subscriber can be assigned a Private User Identity by the home IMS operator. A Private User Identity can be in the format of a NAI (Network Access Identifier), such as “username@operator.com.” A Private User Identity can be used to identify a subscription and authenticate a subscription. Each Private User Identity can be associated with one or more PUIDs (Public User Identifications) that are allocated by the home IMS operator.
An IMS communications session includes session management control connections for session control signaling and media flow connections for media flow between two or more IMS subscribers. IMS subscribers can use a variety of IP-based services in a single communication session.